An ultrasonic-assisted melt crystallization method

Abstract

The application belongs to the technical field of chemical industry, and particularly relates to an ultrasonic-assisted melt crystallization method. The ultrasonic-assisted melt crystallization method sequentially comprises a cooling crystallization process and a sweating process. The cooling crystallization process comprises a first cooling stage and a second cooling stage. The cooling rate of the first cooling stage is greater than that of the second cooling stage. The ultrasonic wave is used to assist the crystallization of the material to be purified at the beginning of the first cooling stage or the beginning of the second cooling stage. The frequency of the ultrasonic wave is reduced when the crystal appears. The application can promote the nucleation of the material by using the ultrasonic wave to disturb the material at the beginning of the first cooling stage or the beginning of the second cooling stage, reduce the impurities in the crystal, shorten the nucleation time, and increase the cooling rate. The frequency of the ultrasonic wave is reduced when the crystal appears, which can improve the integrity of the crystal and the purity of the product.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology, specifically relating to an ultrasonic-assisted melting and crystallization method. Background Technology

[0002] Melt crystallization is an important chemical separation technology with advantages such as low energy consumption, high efficiency, wide application range, environmental friendliness, and low-temperature operation. It is widely used in chemical, pharmaceutical, and food industries. The basic principle of melt crystallization is to heat the raw material liquid at a temperature above its melting point, bringing it to a molten state. Then, through the circulation of a heat exchange medium within cooling plates or tube bundles, the raw material liquid gradually cools and crystallizes outside the plates, achieving separation based on the different melting points of the components in the mixture. Melt crystallization can be divided into two stages: crystallization and sweating. In the crystallization stage, temperature control causes some components in the mixture to crystallize. The driving force of the crystallization process is saturation or supercooling. Due to the differences in melting points of the systems to be separated, and the difficulty for molecules with different shapes or sizes to enter the crystal lattice, the crystals produced by crystallization have a higher purity than the residual liquid. Sweating is a post-processing step to improve the purity of the crystalline phase. In this stage, the temperature of the heat exchange medium is controlled, causing the crystalline layer to gradually heat up. Because impurities are unevenly distributed in the crystalline layer, the parts of the crystalline layer with higher impurity content have lower melting points and will melt into liquid first and be discharged. This also replaces and washes away the residual liquid adhering to the crystals. Crystallization and sweating processes can significantly improve the purity of substances.

[0003] However, melt crystallization has the following drawbacks: the formation of crystallization nuclei is difficult, which not only prolongs the crystallization time but also reduces the crystallization efficiency. Traditional methods typically promote nucleation and improve crystallization efficiency by adding seed crystals, but the seed crystal size and distribution are difficult to control, and new impurities are easily introduced, leading to a decrease in purity. There are also methods that use ultrasound-assisted crystallization; for example, patent document CN104402697A discloses a method for ultrasound-assisted coenzyme Q10 crystallization. 10Introducing ultrasound into the crystallization process effectively promotes nucleation, reduces aggregation, and improves the purity of the crystallized product. The theoretical basis for this is ultrasound-assisted crystallization using the cavitation effect of ultrasound. In a liquid, when the power of the sound wave is large enough and the negative pressure on the liquid is strong enough, the average distance between the molecules of the medium will increase and exceed the limit distance, thereby breaking the liquid and forming cavities. At the moment of intense contraction and collapse of the cavitation cavity, local high pressure and high temperature of thousands of degrees can be generated inside the bubble, thus forming the ultrasonic cavitation phenomenon. It is generally believed that the rapid cooling process of ultrasonic cavitation will create extremely high local supersaturation in the crystallization solution system, promoting crystallization. The propagation of ultrasound in the solution medium can accelerate the effective collision and diffusion of solute molecules, effectively promoting primary nucleation. The microjets generated by cavitation can effectively impact large seed crystals, causing partial breakage and dissolution of large grains, effectively promoting secondary nucleation, promoting the formation of uniform small grains, solving the problem of seed crystal preparation and increasing the number of seed crystals, thus increasing the yield and crystallization rate of crystal growth. The mechanical, thermal, and activation effects caused by ultrasonic cavitation can effectively improve the mass and heat transfer of the solution, thereby promoting the crystallization process and obtaining good crystals.

[0004] However, the purity of the product needs to be further improved by using ultrasonic-assisted crystallization. Summary of the Invention

[0005] In view of this, the present invention provides an ultrasonic-assisted melting and crystallization method to further improve product purity.

[0006] To achieve the above solution, the technical solution of the present invention is as follows:

[0007] This invention provides an ultrasonic-assisted melting and crystallization method, which sequentially includes a cooling crystallization step and a sweating step. The cooling crystallization step includes a first cooling stage and a second cooling stage. The cooling rate of the first cooling stage is greater than the cooling rate of the second cooling stage. Ultrasonic waves are activated at the beginning of the first cooling stage or the beginning of the second cooling stage to assist in the crystallization of the material to be purified, and the frequency of the ultrasonic waves is reduced when crystals begin to appear.

[0008] This application utilizes ultrasound to assist in the crystallization of the material to be purified at the beginning of either the first or second cooling stage. This allows the ultrasonic disturbance to promote material cooling and nucleation, reduce impurities in the crystals, shorten the nucleation time, increase the cooling rate, and improve product purity. Furthermore, using ultrasound to assist in crystallization during the process accelerates melting, lowers the melting temperature, and improves product purity. By reducing the frequency of the ultrasound when crystals begin to appear, the integrity of the crystals can be improved, thereby increasing product purity.

[0009] Optionally, at the beginning of the first cooling stage or the beginning of the second cooling stage, ultrasonic waves with a frequency of 40-50 kHz are used to assist in the crystallization of the material to be purified.

[0010] Optionally, when crystals begin to appear, the frequency of the ultrasound is reduced to 20-30 kHz, preferably 25-30 kHz.

[0011] Specifically, this application can further improve the integrity of the crystals and thus further enhance the purity of the product by setting the frequency of the ultrasound to 20-25 kHz, particularly 25-30 kHz, when the crystals begin to appear.

[0012] Optionally, the power of the ultrasonic wave is 60-80W, preferably 70-80W.

[0013] Specifically, by setting the power of the ultrasonic waves to 60-80W, and especially to 70-80W, this application can reduce the force of crystal particles, increase the growth rate of crystal nuclei, improve the cooling rate, and thus further enhance the purity of the product.

[0014] Optionally, the material to be purified is selected from fluoroethylene carbonate or ethylene carbonate.

[0015] Optionally, the cooling rate in the first cooling stage is less than the cooling rate in the second cooling stage.

[0016] Optionally, the cooling range of the heat exchange medium used in the first cooling stage is 8-11℃, and the cooling range of the heat exchange medium used in the second cooling stage is 15-20℃.

[0017] Optionally, if the material to be purified is fluorocarbonate, the heat exchange medium during the crystallization process is an aqueous solution of ethylene glycol.

[0018] Optionally, the concentration of ethylene glycol in the aqueous ethylene glycol solution is 25wt%-35wt%.

[0019] Optionally, if the material to be purified is ethylene carbonate, the heat exchange medium during the crystallization process is water.

[0020] Optionally, after sweating, the ultrasonic-assisted melting and crystallization method further includes: heating and melting. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] One embodiment of this application provides an ultrasonic-assisted melting and crystallization method, which sequentially includes a cooling crystallization step, a sweating step, and a heating and melting step. The cooling crystallization step includes a first cooling stage and a second cooling stage. The cooling rate of the first cooling stage is greater than the cooling rate of the second cooling stage. At the beginning of the first cooling stage or the beginning of the second cooling stage, an ultrasonic wave with a frequency of 40-50kHz and a power of 60-80W is used to assist in the crystallization of the material to be purified. When crystals begin to appear, the frequency of the ultrasonic wave is reduced to 20-30kHz. The material to be purified is selected from fluoroethylene carbonate or ethylene carbonate.

[0023] The temperature drop in the first cooling stage is less than that in the second cooling stage. The temperature drop of the heat exchange medium used in the first cooling stage is 8-11℃, and the temperature drop of the heat exchange medium used in the second cooling stage is 15-20℃. If the material to be purified is fluoroethylene carbonate, the heat exchange medium during the crystallization process is an aqueous solution of ethylene glycol; if the material to be purified is ethylene carbonate, the heat exchange medium during the crystallization process is water.

[0024] The present invention will be described in detail below through specific examples and embodiments. It should also be understood that the following embodiments are only for specific illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0025] Example 1

[0026] The specific steps of the melt crystallization method for ethylene carbonate (EC) are as follows:

[0027] The molten ethylene carbonate material to be crystallized (purity of 95.00 wt%, tested according to "HG / T 5391-2018 Industrial Ethylene Carbonate") is fed into the static crystallizer;

[0028] Water, the heat exchange medium, is introduced into the crystallizer through the heat exchange medium inlet for cooling and crystallization. During the cooling and crystallization process, the temperature of the heat exchange medium drops rapidly from 43℃ to 32℃ (i.e., the first cooling stage, with a cooling rate of 0.278℃ / min). At this time, the ultrasonic generator is turned on to assist in crystallization. The frequency of the ultrasonic wave is 40kHz and the power of the ultrasonic wave is 80W.

[0029] Next, the temperature of the heat exchange medium was slowly reduced from 32℃ to 16℃ (i.e., the second cooling stage, with a cooling rate of 0.079℃ / min) until crystal nucleation was completed. After holding the temperature for 0.2h, crystallization ended, and the power to the ultrasonic generator was turned off.

[0030] When crystallization begins to occur during the cooling crystallization process, the ultrasonic frequency is adjusted to 30kHz.

[0031] After cooling and crystallization, sweating is induced by raising the temperature to the final temperature of the sweating material at 37°C to expel the sweat.

[0032] After the sweating process is completed, the material is heated to 43°C and completely melted. The resulting product is discharged from the material outlet of the crystallizer, weighed, and sampled. The purity of the product is tested in accordance with "HG / T 5391-2018 Industrial Ethylene Carbonate". The results are shown in Table 1.

[0033] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0034] Example 2

[0035] The difference between this embodiment and Embodiment 1 is that the frequency of the ultrasound is adjusted to 20kHz when crystallization begins to occur during the cooling crystallization process.

[0036] The purity of the product was tested according to "HG / T 5391-2018 Industrial Ethylene Carbonate", and the results are shown in Table 1.

[0037] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0038] Example 3

[0039] The melt crystallization method for fluoroethylene carbonate (FEC) involves the following steps:

[0040] The molten fluoroethylene carbonate material to be crystallized (purity of 95wt%, tested according to "HG / T 4790-2014 Fluoroethylene Carbonate") is fed into the static crystallizer;

[0041] An aqueous solution of ethylene glycol (30wt% concentration) is introduced into the crystallizer through the heat exchange medium inlet for cooling and crystallization. During the cooling and crystallization process, the temperature of the heat exchange medium drops rapidly from 28℃ to 20℃ (i.e., the first cooling stage, with a cooling rate of 0.277℃ / min). At this time, the ultrasonic generator is turned on to assist in crystallization. The frequency of the ultrasonic wave is 40kHz and the power of the ultrasonic wave is 80W.

[0042] Next, the temperature of the heat exchange medium is slowly reduced from 20℃ to 5℃ (i.e., the second cooling stage, with a cooling rate of 0.080℃ / min) until crystal nucleation is complete. After holding the temperature for 0.2h, crystallization ends, and the power to the ultrasonic generator is turned off.

[0043] When crystallization begins to occur during the cooling crystallization process, the ultrasonic frequency is adjusted to 30kHz.

[0044] After cooling and crystallization, sweating is induced by raising the temperature to the final temperature of the sweating material at 37°C to expel the sweat.

[0045] After the sweating process is completed, the product is heated and melted. The resulting product is discharged from the material outlet of the crystallizer, collected, weighed, and sampled. The purity of the product is tested in accordance with "HG / T 4790-2014 Fluorinated Ethylene Carbonate". The results are shown in Table 1.

[0046] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that: at the beginning of the second cooling stage, the ultrasonic generator was turned on to assist crystallization, the ultrasonic frequency was 40kHz, the ultrasonic power was 80W, and the ultrasonic frequency was not adjusted during the cooling crystallization process.

[0049] The purity of the product was tested according to "HG / T 5391-2018 Industrial Ethylene Carbonate", and the results are shown in Table 1.

[0050] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0051] Comparative Example 2

[0052] The difference between this comparative example and Comparative Example 1 is that the ultrasonic generator is turned on at the beginning of the first cooling stage to assist crystallization, the ultrasonic frequency is 30kHz, and the ultrasonic power is 80W.

[0053] The purity of the product was tested according to "HG / T 5391-2018 Industrial Ethylene Carbonate", and the results are shown in Table 1.

[0054] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0055] Comparative Example 3

[0056] The difference between this comparative example and Comparative Example 1 is that the ultrasonic generator was turned on at the beginning of the first cooling stage to assist in crystallization, the ultrasonic frequency was 50kHz, and the ultrasonic power was 80W.

[0057] The purity of the product was tested according to "HG / T 5391-2018 Industrial Ethylene Carbonate", and the results are shown in Table 1.

[0058] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0059] Comparative Example 4

[0060] The difference between this comparative example and Comparative Example 1 is that the ultrasonic generator is turned on at the beginning of the first cooling stage to assist crystallization, the ultrasonic frequency is 40kHz, and the ultrasonic power is 60W.

[0061] The purity of the product was tested according to "HG / T 5391-2018 Industrial Ethylene Carbonate", and the results are shown in Table 1.

[0062] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0063] Comparative Example 5

[0064] The difference between this comparative example and Comparative Example 1 is that the ultrasonic generator is turned on at the beginning of the first cooling stage to assist crystallization, the ultrasonic frequency is 40kHz, and the ultrasonic power is 70W.

[0065] The purity of ethylene carbonate in the product was tested according to "HG / T 5391-2018 Industrial Ethylene Carbonate", and the results are shown in Table 1.

[0066] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0067] Comparative Example 6

[0068] The difference between this comparative example and Comparative Example 1 is that the ultrasonic generator is turned on at the beginning of the first cooling stage to assist crystallization, the ultrasonic frequency is 40kHz, and the ultrasonic power is 90W.

[0069] The purity of the product was tested according to "HG / T 5391-2018 Industrial Ethylene Carbonate", and the results are shown in Table 1.

[0070] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0071] Comparative Example 7

[0072] The difference between this comparative example and Example 1 is that ultrasound was not used.

[0073] The purity of the product was tested according to "HG / T 5391-2018 Industrial Ethylene Carbonate", and the results are shown in Table 1.

[0074] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0075] Comparative Example 8

[0076] The difference between this comparative example and Comparative Example 1 is that the ultrasonic generator is turned on at the beginning of the first cooling stage to assist crystallization, the ultrasonic frequency is 40kHz, and the ultrasonic power is 80W.

[0077] The purity of the product was tested according to "HG / T 5391-2018 Industrial Ethylene Carbonate", and the results are shown in Table 1.

[0078] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0079] Comparative Example 9

[0080] The difference between this comparative example and Example 3 is that the frequency of the ultrasound was not adjusted during the cooling crystallization process.

[0081] The purity of the product was tested according to "HG / T 4790-2014 Fluorinated Ethylene Carbonate", and the results are shown in Table 1.

[0082] The final temperatures of crystallization and melting of the material were measured, and the results are shown in Table 1.

[0083] Table 1 Test Results

[0084]

[0085] As shown in Table 1, compared with Comparative Example 7 (without ultrasound), the melting temperatures of Comparative Example 8 (with ultrasound-assisted crystallization at the beginning of the first cooling stage) and Comparative Example 1 (with ultrasound-assisted crystallization at the beginning of the second cooling stage) were significantly lower, and the product purity was significantly improved. This result indicates that by using ultrasound-assisted crystallization during the crystallization process, this application can utilize wave disturbance to promote material cooling and nucleation, reduce impurities in the crystals, significantly shorten the nucleation time, increase the cooling rate, and thus improve product purity. Furthermore, using ultrasound-assisted crystallization during the crystallization process can accelerate melting, lower the melting temperature, and improve product purity.

[0086] As shown in Table 1, Comparative Example 8 (ultrasound frequency 40kHz, ultrasound power 80W) and Comparative Examples 4-6 (ultrasound frequency 40kHz, ultrasound power 60W, 70W, and 90W respectively) indicate that product purity increases with increasing ultrasound power. However, after the ultrasound power reaches 80W, further increases in ultrasound power do not significantly change product purity. This result suggests that with increasing ultrasound power, crystal particle size gradually decreases, crystal nucleus growth rate gradually increases, and cooling rate significantly improves, thus increasing product purity. When the ultrasound power exceeds 80W, the effect on crystal growth is not significant, and a growth plateau occurs.

[0087] As shown in Table 1, Comparative Examples 2 (ultrasound frequency of 30 kHz), 3 (ultrasound frequency of 50 kHz), and 8 (ultrasound frequency of 40 kHz) reveal, product purity increases with increasing ultrasonic frequency, reaching its highest at 40 kHz. Further increases in ultrasonic frequency lead to a decrease in product purity. This result indicates that excessively high ultrasonic frequencies result in excessive crystal disturbance and incomplete nucleation, while excessively low frequencies cause impurities to remain trapped on the crystal, making removal difficult and ultimately reducing product purity.

[0088] As shown in Table 1, compared with Comparative Example 2 (no adjustment of ultrasonic frequency during cooling crystallization), the purity of the products from Examples 1 (the ultrasonic frequency was adjusted to 30 kHz when crystallization began during cooling crystallization) and 2 (the ultrasonic frequency was adjusted to 20 kHz when crystallization began during cooling crystallization) increased significantly. Furthermore, compared with Example 2 (the ultrasonic frequency was adjusted to 20 kHz when crystallization began during cooling crystallization), the purity of the product from Example 1 (the ultrasonic frequency was adjusted to 30 kHz when crystallization began during cooling crystallization) increased significantly. This result indicates that reducing the ultrasonic frequency at the onset of crystallization better protects the integrity of the crystals and improves product purity. Too high an ultrasonic frequency leads to excessive disturbance, while too low an ultrasonic frequency encapsulates impurities, resulting in a decrease in product purity. Furthermore, comparing Example 3 and Comparative Example 9 shows that reducing the frequency during cooling crystallization can improve the purity of fluoroethylene carbonate. This result indicates that the method of this application is applicable not only to the melt crystallization of ethylene carbonate but also to the melt crystallization of fluoroethylene carbonate, demonstrating a wide range of applicability.

[0089] In summary, this application utilizes ultrasonic-assisted crystallization during the crystallization process. This utilizes wave disturbance to promote material cooling and nucleation, reducing impurities trapped in the crystals, significantly shortening the nucleation time, increasing the cooling rate, and thus improving product purity. With increasing ultrasonic power, the crystal particle size gradually decreases, the crystal nucleus growth rate gradually increases, and the cooling rate significantly improves, thereby increasing product purity. When the power exceeds 80W, the effect on crystal growth is not significant, and a growth plateau occurs. Excessively high ultrasonic frequencies lead to excessive crystal disturbance and incomplete nucleation, while excessively low ultrasonic frequencies result in impurities encapsulating on the crystals, making removal difficult and reducing product purity. Lowering the ultrasonic frequency at the onset of crystallization better protects the integrity of the crystals and improves product purity. Excessively high ultrasonic frequencies cause excessive disturbance, while excessively low ultrasonic frequencies encapsulate impurities, both leading to decreased product purity. This method is applicable to a variety of materials.

[0090] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An ultrasonic-assisted melting and crystallization method, wherein the ultrasonic-assisted melting and crystallization method sequentially includes a cooling crystallization step and a sweating step, the cooling crystallization step including a first cooling stage and a second cooling stage, wherein the cooling rate of the first cooling stage is greater than the cooling rate of the second cooling stage, characterized in that, At the beginning of the first cooling stage or the beginning of the second cooling stage, ultrasonic waves are used to assist in the crystallization of the material to be purified, and the frequency of the ultrasonic waves is reduced when crystals begin to appear. At the beginning of the first or second cooling stage, ultrasonic waves with a frequency of 40-50kHz are used to assist in the crystallization of the material to be purified. When crystals begin to appear, the frequency of the ultrasound is reduced to 20-30 kHz.

2. The ultrasonic-assisted melting and crystallization method as described in claim 1, characterized in that, The power of the ultrasonic wave is 60-80W.

3. The ultrasonic-assisted melting and crystallization method as described in claim 1, characterized in that, The material to be purified is selected from fluoroethylene carbonate or ethylene carbonate.

4. The ultrasonic-assisted melting and crystallization method as described in claim 3, characterized in that, The temperature drop in the first cooling stage is less than that in the second cooling stage.

5. The ultrasonic-assisted melting and crystallization method as described in claim 4, characterized in that, The cooling range of the heat exchange medium used in the first cooling stage is 8-11℃, and the cooling range of the heat exchange medium used in the second cooling stage is 15-20℃.

6. The ultrasonic-assisted melting and crystallization method as described in claim 5, characterized in that, If the material to be purified is fluorocarbonate, the heat exchange medium during the crystallization process is an aqueous solution of ethylene glycol.

7. The ultrasonic-assisted melting and crystallization method as described in claim 5, characterized in that, If the material to be purified is ethylene carbonate, the heat exchange medium during the crystallization process is water.

8. The ultrasonic-assisted melting and crystallization method as described in claim 1, characterized in that, After sweating, the ultrasonic-assisted melting and crystallization method further includes: heating and melting.

Images